If you’re investing time or money in SEO/PPC, you need to know what you’re getting in return. The best measure is your bank account and ROI, but with careful analysis of your visitors and their behaviors, you can increase your bottom line, help redirect efforts to the most profitable website segments, and get more out of each landing page. In this article we discuss web analytics and its usage for your website.
Analytics Products
There are many tools on the web for free and others for reasonable prices. Take your pick.
Google Analytics - Google has a lot of built-in advanced features comparable to expensive analytics tools. The down side is, when you use Google Analytics, you're sharing all your data with Google, and they can do anything with it. For instance, if a certain keyword converts well for you, logically it should convert just as well for other companies, so Google may raise minimum bids for that keyword to make more money.
Sitemeter
Omniture
Efficient Frontier
Yahoo Web Analytics (free, expected to be out soon at the time of this writing).
Mint
Clicky
Clicktracks
Microsoft adCenter Analytics
WebTrends
Piwik
Once you set up your tool, it's time to analyze your traffic!
Google Optimization 
